Rat brain mitochondria were successively submitted to anoxia and reoxygenation. The main mitochondrial functions were assessed at different reoxygenation times. Although the respiratory control ratio decreased, the activity for each one of the enzymes participating in the respiratory chain was not affected. However, during reoxygenation, mitochondrial membrane lipoperoxidation quickly increased and was proportional to the decrease seen in membrane fluidity. Under the same conditions, cytochrome c and cardiolipin were released from mitochondria and their rate of release increased with reoxygenation time. The release of cytochrome c and cardiolipin was followed by the collapse of the membrane potential and it was not inhibited by cyclosporin A. Addition of the antioxidant of-tocopherol abolished all these reoxygenation-induced changes. These data indicate that, in this model, reoxygeriation promotes the uncoupling of respiratory chain, and cytochrome c and cardiolipin releases. These events are not related to the membrane potential collapse but to an oxidative stress. (C) 2003 Elsevier Inc. All rights reserved.